1. Field of the Invention
This invention relates in general to electronic imaging and in particular to a technique for identifying and/or correcting for defects in a solid state imager.
2. Description Relative to the Prior Art
Solid state imaging, such as by means of a charge coupled device (CCD), has found wide acceptance in the video arts for a variety of reasons, among which are lower power consumption, higher sensitivity, and potential cost saving as the technology for producing such devices matures. A typical CCD imager, as representative of the general class of imagers in question, comprises an array of a large number of evenly distributed elemental photosensitive picture elements, i.e. pixels: the greater the number of pixels per imager, the greater the image resolution of the imager. While there is a trend toward employing more and more pixels per imager for image resolution purposes, it is recognized that the greater the number of pixels that an imager has, the greater will be the chance that one or more of the pixels will be bad, thereby possibly rendering the imager useless. Two kinds of pixel defects are generally known to exist in a solid state imager: a "dead" pixel in which little or no image representative photocharge can exist; and a "hot" pixel in which too much photocharge gets accumulated due, for example, to electrical dark current leakage at the pixel. Thus, despite the trend toward more and more pixels per imager, practical design considerations often militate against using more pixels per imager than are absolutely necessary.
Various relatively straightforward techniques are known for obviating the effect of one or more defective pixels in a CCD imager. See, for example, U.S. Pat. No. 4,253,120, issued Feb. 24, 1981, which teaches that, if lower resolving optics for imaging onto a high resolution imager are employed, any given image spot will overlap more than one pixel; and, attendantly, when a pixel is bad, interpolation can be employed to obscure, in real time, the effect of such bad pixel. It is also known to memorize, by use, for example, of a read-only-memory (ROM), the locations of defective pixels of an imager, thereby to produce appropriate correction signals (typically signals corresponding to neutral gray) as substitutes for signals produced by dead and hot pixels . . . this correction technique being, however, one that does not occur in real time. In any event, regardless of which of the aforementioned schemes are employed, correction for defective pixels is usually less than perfect. The latter scheme merely works to dull the effect of a defective pixel; and the former works in a way that, in essence, guesses at what occurs between pixels.
Other art which may be of interest in relation to the present invention may be found in an article from "Television Technology in the 80's" by A. A. Goldberg and J. P. Rossi, pp. 80-88 presented at the SMPTE Conference held Feb. 6-7, 1981.